Image Sensor Device and Method

ABSTRACT

A system and method for forming pixels in an image sensor is provided. In an embodiment, a semiconductor device includes an image sensor including a first pixel region and a second pixel region in a substrate, the first pixel region being adjacent to the second pixel region. A first anti-reflection coating is over the first pixel region, the first anti-reflection coating reducing reflection for a first wavelength range of incident light. A second anti-reflection coating is over the second pixel region, the second anti-reflection coating reducing reflection for a second wavelength range of incident light that is different from the first wavelength range.

PRIORITY CLAIM AND CROSS-REFERENCE

This is a divisional application of U.S. patent application Ser. No.16/568,586, entitled “Image Sensor Device and Method,” filed on Sep. 12,2019, which is a divisional application of U.S. patent application Ser.No. 15/610,034, entitled “Image Sensor Device and Method,” filed on May31, 2017, which is a divisional application of U.S. patent applicationSer. No. 14/996,462, entitled “Image Sensor Device and Method,” whichwas filed on Jan. 15, 2016 and issued as U.S. Pat. No. 9,673,239 on Jun.6, 2017, which applications are incorporated herein by reference.

BACKGROUND

Complementary metal oxide semiconductor image sensors (CIS) generallyutilize a series of photodiodes formed within an array of pixel regionsof a semiconductor substrate in order to sense when light has impactedthe photodiode. Adjacent to each of the photodiodes within each of thepixel regions a transfer transistor may be formed in order to transferthe signal generated by the sensed light within the photodiode at adesired time. Such photodiodes and transfer transistors allow for animage to be captured at a desired time by operating the transfertransistor at the desired time.

The complementary metal oxide semiconductor image sensors may generallybe formed in either a front side illumination configuration or aback-side illumination configuration. In a front-side illuminationconfiguration light passes to the photodiode from the “front” side ofthe image sensor where the transfer transistor has been formed. In aback-side illumination configuration, the transfer transistor, the metallayers, and the dielectric layers are formed on the front side of thesubstrate, and light is allowed to pass to the photodiode from the“back” side of the substrate such that the light hits the photodiodebefore it reaches the transfer transistor, the dielectric layers, or themetal layers. Some configurations of CIS include an anti-reflectioncoating (ARC) that allows more light to reach the photodiode by reducingthe amount of light reflected from the substrate and away from thephotodiode.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A illustrates an image sensor with an array of pixel regions inaccordance with some embodiments.

FIG. 1B illustrates anti-reflection coatings over a first photosensitivediode, a second photosensitive diode, and a third photosensitive diodein a substrate in accordance with some embodiments.

FIG. 1C illustrates a graph of quantum efficiency versus anti-reflectioncoating thickness in accordance with some embodiments.

FIG. 2 illustrates a formation of color filters and microlenses over thesubstrate in accordance with some embodiments.

FIG. 3 illustrates a formation of anti-reflection coatings in accordancewith some embodiments.

FIG. 4 illustrates a formation of anti-reflection coatings comprisingdifferent materials in accordance with some embodiments.

FIG. 5 illustrates a graph of quantum efficiency of a photosensitivediode with different anti-reflection coatings in accordance with someembodiments.

FIGS. 6A-6B illustrate arrays of pixel regions in accordance with someembodiments.

FIG. 7 illustrates a graph of signal-to-noise ratio versus green pixelsize in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

With reference now to FIG. 1A, there is shown an image sensor 100 whichcomprises a grid or array of backside illuminated pixel regions 101. Anexample portion of the array of pixel regions 101 is shown as pixelarray 110. Example pixel regions are shown as a first pixel region 103,a second pixel region 105, and a third pixel region 107. In otherembodiments, the image sensor 100 may be a frontside illuminated type ofimage sensor. The image sensor 100 also may comprise a logic region 109located adjacent to the array of pixel regions 101. The logic region 109may have additional circuitry and contacts for input and outputconnections to and from the array of pixel regions 101. The logic region109 is utilized to provide an operating environment for the pixelregions 101 and to moderate communications between the array of pixelregions 101 and other external devices (not shown).

FIG. 1B illustrates a simplified cross sectional view of adjacent pixelregions including the first pixel region 103, the second pixel region105, and the third pixel region 107 through line A-A′ in FIG. 1A. FIG.1B shows a substrate 111 with the first pixel region 103, the secondpixel region 105, and the third pixel region 107 separated by isolationregions 117. The substrate 111 may comprise a front side 113 and a backside 115 and may be a semiconductor material such as silicon, germanium,diamond, or the like. Alternatively, compound materials such as silicongermanium, silicon carbide, gallium arsenic, indium arsenide, indiumphosphide, silicon germanium carbide, gallium arsenic phosphide, galliumindium phosphide, combinations of these, and the like, with othercrystal orientations, may also be used. Additionally, the substrate 111may comprise a silicon-on-insulator (SOI) substrate. Generally, an SOIsubstrate comprises a layer of a semiconductor material such asepitaxial silicon, germanium, silicon germanium, SOI, silicon germaniumon insulator (SGOI), or combinations thereof. The substrate 111 may bedoped with a p-type dopant, such as boron, gallium, although thesubstrate may alternatively be doped with an n-type dopant, as is knownin the art.

The isolation regions 117 may be located within the substrate 111between the first pixel region 103, the second pixel region 105, and thethird pixel region 107 in order to separate and isolate the first pixelregion 103, the second pixel region 105, and the third pixel region 107.The isolation regions 117 may be shallow trench isolations generallyformed by etching the substrate 111 to form a trench and filling thetrench with dielectric material as is known in the art. The isolationregions 117 may be filled with a dielectric material such as an oxidematerial, a high-density plasma (HDP) oxide, or the like, formed byconventional methods known in the art. Optionally, an oxide liner may beformed along the sidewalls of the isolation regions 117.

A first photosensitive diode 119 may be formed in first pixel region103, a second photosensitive diode 121 may be formed in second pixelregion 105, and a third photosensitive diode 123 may be formed in thirdpixel region 107. The first photosensitive diode 119, the secondphotosensitive diode 121, and the third photosensitive diode 123 may beutilized to generate a signal related to the intensity or brightness oflight that impinges on the respective photosensitive diode. In anembodiment, the first photosensitive diode 119, the secondphotosensitive diode 121, and the third photosensitive diode 123 maycomprise n-type doped regions 125 formed in the substrate 111 (which inthis embodiment may be a p-type substrate) and also may comprise heavilydoped p-type doped regions 127 formed on the surface of the n-type dopedregions 125 to form a p-n-p junction.

The n-type doped regions 125 may be formed, e.g., using aphotolithographic masking and implantation process. For example, a firstphotoresist (not shown in FIG. 1B) may be placed on the substrate 111.The first photoresist, may comprise a conventional photoresist material,such as a deep ultra-violet (DUV) photoresist, and may be deposited onthe surface of the substrate 111, for example, by using a spin-onprocess to place the first photoresist. However, any other suitablematerial or method of forming or placing the first photoresist mayalternatively be utilized. Once the first photoresist has been placed onthe substrate 111, the first photoresist may be exposed to energy, e.g.light, through a patterned reticle in order to induce a reaction inthose portions of the first photoresist exposed to the energy. The firstphotoresist may then be developed, and portions of the first photoresistmay be removed, exposing a portion of the substrate 111 where the firstphotosensitive diode 119, the second photosensitive diode 121, and thethird photosensitive diode 123 are desired to be located.

Once the first photoresist has been placed and developed, the heavilydoped n-type doped regions 125 may be formed by implanting n-typedopants (e.g., phosphorous, arsenic, antimony, or the like) through thefirst photoresist. In an embodiment the n-type doped regions 125 may beimplanted such that their concentration of between about 1e15 atom/cm³and about 1e20 atom/cm³, such as about 8e15 atom/cm³. However, anysuitable alternative concentration for the heavily doped n-type dopedregions 125 may alternatively be utilized.

After the n-type doped regions 125 have been formed (e.g., through theimplantation process), the p-type doped regions 127 may be formed using,e.g., an ion implantation process using the first photoresist as a mask.The p-type doped regions 127 may be formed to extend into the substrate111 between about 1 μm and about 4 μm. Additionally, the p-type dopedregions 127 may be formed to have a concentration of between about 1e15atom/cm³ and about 5e19 atom/cm³, such as about 1e16 atom/cm³. Once thefirst photosensitive diode 119, the second photosensitive diode 121, andthe third photosensitive diode 123 have been formed, the firstphotoresist may be removed. In an embodiment, the first photoresist maybe removed using a process such as ashing.

Further, as one of ordinary skill in the art will recognize the firstphotosensitive diode 119, the second photosensitive diode 121, and thethird photosensitive diode 123 described above are merely one type ofphotosensitive diodes that may be used in the embodiments. Any suitablephotodiode may be utilized with the embodiments, and all of thesephotodiodes are intended to be included within the scope of theembodiments. Additionally, the precise methods or order of stepsdescribed above may be modified, such as by forming the p-type dopedregions 127 prior to the formation of the n-type doped regions 125,while still remaining within the scope of the embodiments.

A first transistor 129 a, a second transistor 129 b, and a thirdtransistor 129 c may be formed adjacent to the first photosensitivediode 119, the second photosensitive diode 121, and the thirdphotosensitive diode 123, in the first pixel region 103, the secondpixel region 105, and the third pixel region 107, respectively. Thefirst transistor 129 a, the second transistor 129 b, and the thirdtransistor 129 c may be transfer transistors. However, the firsttransistor 129 a, the second transistor 129 b, and the third transistor129 c are also merely representative of the many types of functionaltransistors that may be utilized within the first pixel region 103, thesecond pixel region 105, and the third pixel region 107. For example,while the first transistor 129 a, the second transistor 129 b, and thethird transistor 129 c are illustrated in FIG. 1B as transfertransistors, embodiments may additionally include other transistorslocated within the first pixel region 103, the second pixel region 105,and the third pixel region 107, such as reset transistors, sourcefollower transistors, or select transistors. These transistors may bearranged, for example, to form a four transistor CMOS image sensor(CIS). All suitable transistors and configurations that may be utilizedin an image sensor are fully intended to be included within the scope ofthe embodiments.

The first transistor 129 a, the second transistor 129 b, and the thirdtransistor 129 c may comprise gate stacks that may be formed over thesubstrate 111. The gate stacks may each comprise a gate dielectric 131and a gate electrode 133. The gate dielectrics 131 and gate electrodes133 may be formed and patterned on the substrate 111 by any suitableprocess known in the art. The gate dielectrics 131 may be a high-kdielectric material, such as silicon oxide, silicon oxynitride, siliconnitride, an oxide, a nitrogen-containing oxide, aluminum oxide,lanthanum oxide, hafnium oxide, zirconium oxide, hafnium oxynitride, acombination thereof, or the like. The gate dielectrics 131 may have arelative permittivity value greater than about 4.

In an embodiment in which the gate dielectrics 131 comprise an oxidelayer, the gate dielectrics 131 may be formed by any oxidation process,such as wet or dry thermal oxidation in an ambient comprising an oxide,H₂O, NO, or a combination thereof, or by chemical vapor deposition (CVD)techniques using tetra-ethyl-ortho-silicate (TEOS) and oxygen as aprecursor. In one embodiment, the gate dielectrics 131 may be betweenabout 10 Å to about 150 Å in thickness, such as 100 Å in thickness.

The gate electrodes 133 may comprise a conductive material, such as ametal (e.g., tantalum, titanium, molybdenum, tungsten, platinum,aluminum, hafnium, ruthenium), a metal silicide (e.g., titaniumsilicide, cobalt silicide, nickel silicide, tantalum silicide), a metalnitride (e.g., titanium nitride, tantalum nitride), dopedpoly-crystalline silicon, other conductive materials, or a combinationthereof. In one example, amorphous silicon is deposited andrecrystallized to create poly-crystalline silicon (poly-silicon). In anembodiment in which the gate electrodes 133 is poly-silicon, the gateelectrodes 133 may be formed by depositing doped or undoped poly-siliconby low-pressure chemical vapor deposition (LPCVD) to a thickness in therange of about 100 Å to about 2,500 Å, such as 1,200 Å.

Spacers 135 may be formed on the sidewalls of the gate dielectrics 131and the gate electrodes 133. The spacers 135 may be formed by blanketdepositing a spacer layer (not shown) on the previously formedstructure. The spacer layer may comprise SiN, oxynitride, SiC, SiON,oxide, and the like, and may be formed by commonly used methods such aschemical vapor deposition (CVD), plasma enhanced CVD, sputter, and othermethods known in the art. The spacer layer is then patterned to form thespacers 135, such as by anisotropically etching to remove the spacerlayer from the horizontal surfaces of the structure.

Source/drain regions 137 may be formed in the substrate 111 on anopposing side of the gate dielectrics 131 from the first photosensitivediode 119, the second photosensitive diode 121, and the thirdphotosensitive diode 123. In an embodiment in which the substrate 111 isa p-type substrate, the source/drain regions 137 may be formed byimplanting appropriate n-type dopants such as phosphorous, arsenic orantimony. The source/drain regions 137 may be implanted using the gateelectrodes 133 and the spacers 135 as masks to form lightly dopedsource/drain (LDD) regions 139 and heavily doped source/drain regions141.

It should be noted that one of ordinary skill in the art will realizethat many other processes, steps, or the like may be used to form thesource/drain regions 137 and the first photosensitive diode 119, thesecond photosensitive diode 121, and the third photosensitive diode 123.For example, one of ordinary skill in the art will realize that aplurality of implants may be performed using various combinations ofspacers and liners to form the source/drain regions 137 and the firstphotosensitive diode 119, the second photosensitive diode 121, and thethird photosensitive diode 123 having a specific shape or characteristicsuitable for a particular purpose. Any of these processes may be used toform the source/drain regions 137 and the first photosensitive diode119, the second photosensitive diode 121, and the third photosensitivediode 123, and the above description is not meant to limit theembodiments to the steps presented above.

Once the first transistor 129 a, the second transistor 129 b, and thethird transistor 129 c have been formed, a first inter-layer dielectric(ILD) layer 143 may be formed over the first pixel region 103, thesecond pixel region 105, and the third pixel region 107 and contacts 145may be formed through the first ILD layer 143. The first ILD layer 143may comprise a material such as boron phosphorous silicate glass (BPSG),although any suitable dielectrics may be used for either layer. Thefirst ILD layer 143 may be formed using a process such as PECVD,although other processes, such as LPCVD, may alternatively be used. Thefirst ILD layer 143 may be formed to a thickness of between about 100 Åand about 3,000 Å.

The contacts 145 may be formed through the first ILD layer 143 withsuitable photolithography and etching techniques. In an embodiment afirst photoresist material is utilized to create a patterned mask todefine contacts 145. Additional masks, such as a hardmask, may also beused. An etching process, such as an anisotropic or isotropic etchprocess, is performed to etch the first ILD layer 143.

Contacts 145 may then be formed so as to contact the substrate 111 andthe gate electrodes 133. The contacts 145 may comprise abarrier/adhesion layer (not individually shown in FIG. 1B) to preventdiffusion and provide better adhesion for the contacts 145. In anembodiment, the barrier layer is formed of one or more layers oftitanium, titanium nitride, tantalum, tantalum nitride, or the like. Thebarrier layer may be formed through chemical vapor deposition, althoughother techniques could alternatively be used. The barrier layer may beformed to a combined thickness of about 50 Å to about 500 Å.

The contacts 145 may be formed of any suitable conductive material, suchas a highly-conductive, low-resistive metal, elemental metal, transitionmetal, or the like. In an exemplary embodiment the contacts 145 areformed of tungsten, although other materials, such as copper, couldalternatively be utilized. In an embodiment in which the contacts 145are formed of tungsten, the contacts 145 may be deposited by CVDtechniques known in the art, although any method of formation couldalternatively be used.

After the contacts 145 are formed, further processing of the front side113 of the substrate 111 may be performed. This processing may compriseforming various conductive and dielectric layers (collectively referredto in FIG. 1B by the reference number 147) in order to forminterconnections between the individually formed devices to each other.These interconnections may be made through any suitable formationprocess (e.g., lithography with etching, damascene, dual damascene, orthe like) and may be formed using suitable conductive materials such asaluminum alloys, copper alloys, or the like.

Additionally, once the interconnections have been formed over the firstILD layer 143, a passivation layer 149 may be formed in order to protectthe underlying layers from physical and chemical damage. The passivationlayer 149 may be made of one or more suitable dielectric materials suchas silicon oxide, silicon nitride, low-k dielectrics such as carbondoped oxides, extremely low-k dielectrics such as porous carbon dopedsilicon dioxide, combinations of these, or the like. The passivationlayer 149 may be formed through a process such as chemical vapordeposition (CVD), although any suitable process may be utilized.

FIG. 1B also illustrates a placement of the substrate 111 on a carrierwafer 151 and further processing on the back side 115 of the substrate111 that may be performed after the processing on the front side 113 ofthe substrate 111. The carrier wafer 151 may be utilized to providesupport and protection to the structures on the front side 113 of thesubstrate 111 while the back side 115 is further processed, and thecarrier wafer 151 may comprise a material such as glass, silicon, glassceramics, combinations of these, or the like. The substrate 111 may beattached to the carrier wafer 151 using, e.g., an adhesive (notindividually illustrated in FIG. 1B), although any suitable method ofattaching the substrate 111 to the carrier wafer 151 may alternativelybe utilized.

Alternatively, the substrate 111 may be wafer bonded to another wafer(not illustrated) instead of the carrier wafer 151. In this embodimentthe substrate 111 may be physically and electrically connected throughthe conductive and dielectric layers 147 and the passivation layer 149to another wafer in order to provide signals and/or power between thesubstrate 111 and the other wafer. This and any other method ofprotecting the front side 113 of the substrate 111 may alternatively beutilized, and all such methods are fully intended to be included withinthe scope of the embodiment.

Once the substrate 111 has been placed on the carrier wafer 151, theback side 115 of the substrate 111 may be processed further. In anembodiment, the thickness of the back side 115 of the substrate 111 maybe reduced or thinned. Thinning reduces the distance that light travelsthrough the back side 115 of the substrate 111 before it reaches thefirst photosensitive diode 119, the second photosensitive diode 121, orthe third photosensitive diode 123. The thinning of the back side 115 ofthe substrate 111 may be performed using a removal process such aschemical mechanical polishing (CMP). In a CMP process, a combination ofetching materials and abrading materials are put into contact with theback side 115 of the substrate 111 and a grinding pad (not shown) isused to grind away the back side 115 of the substrate 111 until adesired thickness is achieved. However, any suitable process forthinning the back side 115 of the substrate 111, such as etching or acombination of CMP and etching, may alternatively be used. The back side115 of the substrate 111 may be thinned so that the substrate 111 has athickness of between about 2 μm and about 2.3 μm.

FIG. 1B illustrates the formation of a first ARC 161, a second ARC 171,and a third ARC 181 over the back side 115 of the substrate 111. In anembodiment, the first ARC 161, the second ARC 171, and the third ARC 181may be used to reduce the amount of incident light reflected away fromthe first photosensitive diode 119, the second photosensitive diode 121,and the third photosensitive diode 123, and thus allow more light toimpinge on the first photosensitive diode 119, the second photosensitivediode 121, and the third photosensitive diode 123. In this manner, theefficiency of the image sensor 100 may be increased, and thesignal-to-noise ratio of the image sensor 100 may also be increased.

In an embodiment, the first ARC 161, the second ARC 171, and the thirdARC 181 may be configured to reduce reflection for specific colors(i.e., specific wavelengths or wavelength ranges) of incident light. Forexample, the first ARC 161, the second ARC 171, and the third ARC 181may be configured to reduce reflection for wavelengths of lightcorresponding to one of the primary colors (blue, green, red). Each ofthe first ARC 161, the second ARC 171, and the third ARC 181 maycomprise one or more layers of different thicknesses and/or one or morelayers of different materials, as discussed below.

In an embodiment, the first ARC 161 may be formed over the back side 115of the substrate 111 in the first pixel region 103. The first ARC 161may be formed by forming a first sublayer 163 and a second sublayer 165.The first sublayer 163 and the second sublayer 165 may be formed througha process such as CVD, PECVD, or combinations of these. The firstsublayer 163 and the second sublayer 165 may be made of one or moresuitable dielectric materials such as silicon oxide, silicon nitride,high-k dielectrics, combinations of these, or the like. For example, thefirst sublayer 163 may be a material such as silicon oxide, although anyother suitable material may alternatively be utilized. The firstsublayer 163 may be formed to a first thickness t₁ of between about 20 Åand about 5000 Å, such as about 500 Å. In some embodiments, the firstsublayer 163 may be patterned over the first pixel region 103 using asuitable photolithographic masking and etching process.

Once the first sublayer 163 has been formed over the first pixel region103, the second sublayer 165 may be formed over the first sublayer 163.The second sublayer 165 may be a different material than the firstsublayer 163. For example, in some embodiments the first sublayer 163 issilicon oxide and the second sublayer 165 is silicon nitride. The secondsublayer 165 may be formed to a second thickness t₂ that is differentfrom the first thickness t₁ of the first sublayer 163. The secondsublayer 165 may be formed to a thickness t₂ of between about 20 Å andabout 5000 Å, such as about 500 Å.

In some embodiments, after the second sublayer 165 is formed over thefirst sublayer 163, over the third sublayer 173 (after the thirdsublayer 173 has been formed as further described below), and over thefifth sublayer 183 (after the fifth sublayer 183 has been formed asfurther described below), the second sublayer 165 may be planarized orthinned to a desired thickness (e.g., second thickness t₂). For example,the second sublayer 165 may be deposited to a thickness greater than thesecond thickness t₂ and then thinned to the second thickness t₂. Thethinning of the second sublayer 165 may be performed using a proceduresuch as CMP, etching, or another procedure or combination of procedures.

In other embodiments, the second sublayer 165 may be patterned over thefirst sublayer 163 in first pixel region 103 using a suitablephotolithographic masking and etching process. The photolithographicprocess for forming the second sublayer 165 may use the samephotolithographic mask as used for forming the first sublayer 163 or adifferent photolithographic mask.

In other embodiments, the first ARC 161 may comprise fewer layers (e.g.,one of the first sublayer 163 or the second sublayer 165) or more layers(e.g., three or more sublayers). To reduce reflection, othercombinations of layer thicknesses, numbers of layers, and layermaterials are possible. The anti-reflection properties of the first ARC161 (e.g., wavelength range, amount of reflection reduction, or otherproperties) may be determined by the material and the first thickness t₁of the first sublayer 163 and the material and the second thickness t₂of the second sublayer 165. For example, in one embodiment the firstsublayer 163 of the first ARC 161 may comprise silicon oxide and thesecond sublayer 165 may comprise a nitride such as SiN. Other pairs ofdifferent materials for the first sublayer 163 and the second sublayer165 may also be used such as combinations of oxide and SiC, oxide andSiN, Al₂O₃ and SiN, HfO₂ and SiN, respectively, or other pairs of theseor other materials.

In some embodiments, the first sublayer 163 and the second sublayer 165may be the same material. In some embodiments, the first ARC 161comprises three sublayers having a combination of materials such as alayer of oxide, a layer of SiN, and another layer of oxide, acombination such as a layer of oxide, a layer of SiC, and a layer ofSiN, a combination such as a layer of Al₂O₃, a layer of HfO₂, and alayer of plasma-enhanced silicon nitride (PESN), or other combinationsof these or other materials. The oxide may be a silicon oxide (e.g., asilicon oxide formed from remote plasma oxidation (RPO), a silicon oxidelayer formed from TEOS, a silicon-rich oxide (SRO), or another type) oranother type of oxide. The examples provided herein are not intended tolimit the scope of this disclosure.

As shown in FIG. 1B, the example image sensor 100 may also include asecond ARC 171 over the second pixel region 105. The second ARC 171 maybe formed in a similar manner to the first ARC 161. As such, the secondARC 171 may comprise a third sublayer 173 with a third thickness t₃ anda fourth sublayer 175 with a fourth thickness t₄. The third thickness t₃and the fourth thickness t₄ may have thicknesses of between about 20 Åand about 5000 Å, such as about 500 Å. The composition and/or thirdthickness t₃ of the third sublayer 173 and the composition and/or fourththickness t₄ of the fourth sublayer 175 in the second ARC 171 may bespecified to reduce reflection for a specific color of light. The secondARC 171 may be formed to reduce reflection for colors of incident lightdifferent than the first ARC 161. For example, the first ARC 161 may beformed to reduce reflection for blue light incident on first pixelregion 103, and the second ARC 171 may be formed to reduce reflectionfor green light incident on second pixel region 105.

In some embodiments, the third thickness t₃ of the third sublayer 173 inthe second ARC 171 may be greater than the first thickness t₁ of thefirst sublayer 163 in the first ARC 161. For example, the thirdthickness t₃ may be between about 20 nm and about 300 nm, such as about80 nm and the first thickness t₁ may be between about 15 nm and about295 nm, such as about 50 nm. In some embodiments, the fourth thicknesst₄ of the fourth sublayer 175 in the second ARC 171 is less than thesecond thickness t₂ of the second sublayer 165 in the first ARC 161. Forexample, the fourth thickness t₄ may be between about 20 nm and about300 nm, such as about 50 nm and the second thickness t₂ may be betweenabout 25 nm and about 305 nm, such as about 80 nm. In some embodiments,the second ARC 171 may comprise one layer or three or more sublayers.

As shown in FIG. 1B, the example image sensor 100 may also include athird ARC 181 over the third pixel region 107. The third ARC 181 may beformed in a similar manner to the first ARC 161 and/or the second ARC171. As such, the third ARC 181 may comprise a fifth sublayer 183 with afifth thickness t_(s) and a sixth sublayer 185 with a sixth thicknesst₆. The composition and/or fifth thickness t_(s) of the fifth sublayer183 and the composition and/or sixth thickness t₆ of the sixth sublayer185 in the third ARC 181 may be specified to reduce reflection for aspecific color of light. The third ARC 181 may be formed to reducereflection for colors of incident light different than the first ARC 161or the second ARC 171. For example, the first ARC 161 may be formed toreduce reflection for blue light incident on first pixel region 103, thesecond ARC 171 may be formed to reduce reflection for green lightincident on second pixel region 105, and the third ARC 181 may be formedto reduce reflection for red light incident on the third pixel region107.

In some embodiments, the fifth thickness t_(s) of the fifth sublayer 183in the third ARC 181 may be greater than the first thickness t₁ of thefirst sublayer 163 in the first ARC 161 and/or greater than the thirdthickness t₃ of the third sublayer 173 in the second ARC 171. Forexample, the fifth thickness t_(s) may be about 80 nm, the thirdthickness t₃ may be about 60 nm, and the first thickness t₁ may be about50 nm. In some embodiments, the sixth thickness t₆ of the sixth sublayer185 in the third ARC 181 is less than the second thickness t₂ of thesecond sublayer 165 in the first ARC 161 and/or the fourth thickness t₄of the fourth sublayer 175 in the second ARC 171. For example, thesecond thickness t₂ may be about 80 nm, the fourth thickness t₄ may beabout 60 nm, and the sixth thickness t₆ may be about 50 nm. In someembodiments, the third ARC 181 may comprise one layer or three or moresublayers.

In some embodiments, the second sublayer 165, the fourth sublayer 175,and the sixth sublayer 185 are formed separately, for example usingthree separate photolithographic masking and etching processes. In someembodiments, the second sublayer 165, the fourth sublayer 175, and thesixth sublayer 185 are formed together, for example with a singledeposition. In some cases, the second sublayer 165, the fourth sublayer175, and the sixth sublayer 185 are planarized or thinned to the sameheight above the substrate 111. The thinning may be performed using aprocedure such as CMP, etching, or another procedure or combination ofprocedures. For example, the second sublayer 165, the fourth sublayer175, and the sixth sublayer 185 may be thinned such that the totalthickness of the first ARC 161, the second ARC 171, and the third ARC181 is the same. In some embodiments, one or more of the first ARC 161,the second ARC 171, and the third ARC 181 may comprise a differentnumber of sublayers. For example, the first ARC 161 may comprise onelayer and second ARC 171 may comprise two layers.

FIG. 1C illustrates a graph 190 showing an example simulation of thequantum efficiency (QE) of a photosensitive diode for different colorsof light (blue, green, red) and for different thicknesses ofanti-reflection coatings (ARCs). For the simulation of graph 190, theARC comprises a sublayer of silicon nitride over silicon oxide, withx-axis indicating the thickness of the silicon nitride layer. As graph190 shows, the QE of the photodiode for each color varies with thethickness of the silicon nitride sublayer, and a single sublayerthickness does not correspond to an optimal QE for all colors. As shownin FIG. 1C, blue light QE has a maximum at a sublayer thickness of about50 nm (near the first point 191), green light QE has a maximum at asublayer thickness of about 60 nm (near the second point 193), and redlight QE has a maximum at a sublayer thickness of about 80 nm (near thethird point 195). Thus, an ARC comprising a single sublayer thickness ofa single material will not necessarily correspond to a QE maximum formultiple colors of light, and pixel regions with different ARCproperties for different pixel regions may improve QE for an imagesensor.

FIG. 2 illustrates the formation of a first color filter 201, a secondcolor filter 203, and a third color filter 205 on the back side 115 ofthe substrate 111 over the first ARC 161, the second ARC 171, and thethird ARC 181, respectively. FIG. 2 also illustrates the formation of afirst microlens 207, a second microlens 209, and a third microlens 211over the first color filter 201, the second color filter 203, and thethird color filter 205, respectively. The first color filter 201, thesecond color filter 203, and the third color filter 205 may eachcomprise individual filters for one of the primary colors (e.g., blue,green, red) and may be positioned to filter the light that will impingeupon the first photosensitive diode 119, the second photosensitive diode121, and the third photosensitive diode 123. The first color filter 201,the second color filter 203, and the third color filter 205 may eachcorrespond to the properties of the first ARC 161, the second ARC 171,and the third ARC 181. For example, in the first pixel region 103, thefirst color filter 201 may permit blue light and the first ARC 161 mayreduce reflections for blue light. Similarly, in the second pixel region105, the second color filter 203 may permit green light and the secondARC 171 may reduce reflections for green light, and in the third pixelregion 107, the third color filter 205 may permit red light and thethird ARC 181 may reduce reflections for red light. The first colorfilter 201, the second color filter 203, and the third color filter 205may be part of an array pattern of color filters. For example, the firstcolor filter 201, the second color filter 203, and the third colorfilter 205 may be part of a Bayer RGB pattern, a Yotsuba CRGB pattern,or any other suitable pattern for the location of color filters over animage sensor 100. In some embodiments, the first color filter 201, thesecond color filter 203, and the third color filter 205 may be part ofthe pixel array 110, shown in FIG. 1A.

One or more of the first color filter 201, the second color filter 203,and the third color filter 205 may comprise a polymeric material orresin, such as a polymeric polymer, which includes colored pigments. Inan embodiment in which polymeric polymers are utilized to form the firstcolor filter 201, the second color filter 203, and the third colorfilter 205, each of the first color filter 201, the second color filter203, and the third color filter 205 may be formed over the substrate 111using a process such as spin coating. After spin coating a polymericmaterial over the substrate 111, the material may be patterned to formthe first color filter 201, the second color filter 203, and/or thethird color filter 205 using a suitable photolithographic masking andetching process. Any other suitable method for forming the first colorfilter 201, the second color filter 203, and/or the third color filter205 may alternatively be utilized.

The first microlens 207, the second microlens 209, and the thirdmicrolens 211 may be formed over the first color filter 201, the secondcolor filter 203, and the third color filter 205 by first applying andpatterning a positive type photoresist (not shown). Once formed, thepatterned photoresist may then be baked to round the photoresist intothe first microlens 207, the second microlens 209, and the thirdmicrolens 211. The first microlens 207, the second microlens 209, andthe third microlens 211 may be used to focus impinging light moredirectly onto the first photosensitive diode 119, the secondphotosensitive diode 121, and the third photosensitive diode 123,respectively.

FIG. 3 illustrates an embodiment of an example image sensor comprising afourth ARC 301 and a fifth ARC 303. The fourth ARC 301 is over both thefirst pixel region 103 and the second pixel region 105 and comprises aseventh sublayer 305 over an eighth sublayer 307. The fifth ARC 303 isover the third pixel region 107 and comprises the seventh sublayer 305.

The fourth ARC 301 and the fifth ARC 303 are formed by forming theseventh sublayer 305 over the back side 115 of the substrate 111. Theseventh sublayer 305 may be formed over the first pixel region 103, thesecond pixel region, 105, and the third pixel region 107, as shown inFIG. 3. The seventh sublayer 305 has a seventh thickness of t₇ ofbetween about 20 Å and about 5000 Å, such as about 300 Å. The seventhsublayer 305 may be formed through a process such as CVD, PECVD, thermaloxidation or combinations of these and made of one or more suitabledielectric materials such as silicon oxide, silicon nitride, high-kdielectric, combinations of these, or the like. In an embodiment, theseventh sublayer 305 may be patterned over the first pixel region 103and the second pixel region 105 using a suitable photolithographicmasking and etching process. In an embodiment, the seventh sublayer 305may be formed over one pixel region (e.g., over the first pixel region103), over two pixel regions (e.g., over both the first pixel region 103and the second pixel region 105), or over another number of pixelregions.

The eighth sublayer 307 may be formed over the seventh sublayer 305. Theeighth sublayer 307 may be formed having an eighth thickness of t₈ ofbetween about 20 Å and about 5000 Å, such as about 300 Å. In theembodiment shown in FIG. 3, the eighth sublayer 307 is formed over boththe first pixel region 103 and the second pixel region 105, and not overthe third pixel region 107. The eighth sublayer 307 may be formed in aprocess similar to that of the seventh sublayer 305, and may be the samematerial as the seventh sublayer 305 or a different material.

As shown in the embodiment of FIG. 3, the first pixel region 103 and thesecond pixel region 105 both are covered by the fourth ARC 301, whichcomprises both the seventh sublayer 305 with a seventh thickness t₇ andthe eighth sublayer 307 with an eighth thickness t₈. Thus, the totalthickness of the fourth ARC 301 is the sum of the seventh thickness t₇and the eighth thickness t₈. The third pixel region 107 is covered bythe fifth ARC 303, which comprises the seventh sublayer 305, and thusthe total thickness of the fifth ARC 303 is the seventh thickness t₇.The first pixel region 103 and the second pixel region 105 thus bothcomprise the fourth ARC 301 that reduces reflection over a first rangeof incident light wavelengths. The third pixel region 107 comprises thefifth ARC 303 that, having a different thickness, reduces reflectionover a different range of incident light wavelengths than the fourth ARC301. For example, the fourth ARC 301 may reduce reflection for twocolors of light (e.g., blue and green, blue and red, or green and red)and the fifth ARC 303 may reduce reflection for another color of light(e.g., red, green, or blue).

In an embodiment, an additional third sublayer (not shown) may beformed. The additional third sublayer may be formed over a single pixelregion (e.g., over the first pixel region 103, the second pixel region105, or the third pixel region 107), or over multiple pixel regions(e.g., over both the first pixel region 103 and the second pixel region105, over other combinations of pixel regions, or over all pixelregions). The additional third sublayer may be the same material as theseventh sublayer 305 and/or the eighth sublayer 307 or be a differentmaterial. In other embodiments, the seventh sublayer 305 and/or theeighth sublayer 307 may be silicon oxide, and the additional third layermay be a material such as silicon oxide, SiN, SiC, Al₂O₃, a layer ofHfO₂, a high-k dielectric, combinations of these, or the like. Theadditional third sublayer may have a thickness of between about 20 Å andabout 5000 Å, such as about 300 Å.

In other embodiments, more than three sublayers may be formed, and theARC over a pixel region may comprise more than three sublayers. In thismanner, different ARCs may be optimized for different colors of lightfor different pixel regions. A single ARC may be optimized for more thanone color of light and formed over more than one pixel region.

A fourth color filter 311, a fifth color filter 313, and a sixth colorfilter 315 and the first microlens 207, the second microlens 209, andthe third microlens 211 may be formed in the manner described previouslywith regard to FIG. 2. The ninth thickness t₉ of the fourth color filter311, the tenth thickness t₁₀ of the fifth color filter 313, and theeleventh thickness t₁₁ of the sixth color filter 315 may both be thesame or may each have a thickness of between about 300 nm and about 1000nm. In another embodiment and as shown in FIG. 3, the ninth thickness t₉and the tenth thickness t₁₀ may be about 600 nm, but the elevenththickness t₁₁ may have a greater thickness of about 700 nm. In otherembodiments, the ninth thickness t₉, the tenth thickness, and theeleventh thickness t₁₁ may have the same thickness or have differentthicknesses in any suitable combination.

FIG. 4 illustrates an embodiment of a sixth ARC 401, a seventh ARC 403,and an eighth ARC 405. In this embodiment, each of the sixth ARC 401,the seventh ARC 403, and the eighth ARC 405 comprise different materialswith different optical properties. For example, the sixth ARC 401, theseventh ARC 403, and the eighth ARC 405 may be formed through a processsuch as CVD, PECVD, thermal oxidation or combinations of these and madeof one or more suitable dielectric materials such as silicon oxide,silicon nitride, high-k dielectrics, combinations of these, or the like.For example, the sixth ARC 401 may be silicon nitride, the seventh ARC403 may be silicon oxide, and the eighth ARC 405 may be a high-kdielectric. Other materials and combinations of materials are possible.

As shown in FIG. 4, the sixth ARC 401, the seventh ARC 403, and theeighth ARC 405 may have the same thickness, though in other embodimentsone or more of the sixth ARC 401, the seventh ARC 403, and the eighthARC 405 may have different thicknesses. For example, the sixth ARC 401,the seventh ARC 403, and the eighth ARC 405 may have a thickness betweenabout 20 Å and about 5000 Å, such as about 500 Å.

The sixth ARC 401, the seventh ARC 403, and the eighth ARC 405 may beformed over the first pixel region 103, the second pixel region 105, andthe third pixel region 107, respectively, using a suitable depositionand photolithographic masking and etching process. For example, thesixth ARC 401 may be formed by depositing material over the substrate111 and then patterning the material to form the sixth ARC 401 over thefirst pixel region 103 using photolithographic and etching techniques.Subsequently, a second material may be deposited and patterned to formthe seventh ARC 403 over the second pixel region 105, and then a thirdmaterial may be deposited and patterned to form the eighth ARC 405 overthe third pixel region 107.

In some embodiments, a layer of a particular material may be formed overmore than one pixel region. For example, a first material may be formedand patterned to form a single ARC over both the first pixel region 103and the second pixel region 105. Then, a second material may be formedand patterned to form an ARC over the third pixel region 107. In someembodiments, one or more of the sixth ARC 401, the seventh ARC 403, andthe eighth ARC 405 may comprise multiple sublayers of similar ordifferent materials. These are examples; other configurations of ARCswith different materials formed over different pixel regions arepossible.

By having different optical properties, each of the sixth ARC 401, theseventh ARC 403, and the eighth ARC 405 may reduce reflection for adifferent color of incident light. For example, three differentmaterials may be selected for the sixth ARC 401, the seventh ARC 403,and the eighth ARC 405 to reduce reflection for blue, green, and redlight, respectively. Each of the sixth ARC 401, the seventh ARC 403, andthe eighth ARC 405 may have a different index of refraction betweenabout 1.4 to 5. For example, the sixth ARC 401, the seventh ARC 403, andthe eighth ARC 405 may each have a thickness of 500 Å, but the sixth ARC401 may have a first refractive index of 1.5 to reduce reflection ofblue light, the seventh ARC 403 may have a second refractive index of1.9 to reduce reflection of green light, and the eighth ARC 405 may havea third refractive index of 2.2 to reduce reflection of red light.

In some embodiments, the sixth ARC 401, the seventh ARC 403, and theeighth ARC 405 may comprise the same material with differentcompositions that provide different optical properties. In thisembodiment, the different optical properties may be achieved by usingdifferent formation conditions such as flow rate (e.g. precursor flowrate), doping concentration, temperature, pressure, or other conditions.The sixth ARC 401, the seventh ARC 403, and the eighth ARC 405 maycomprise the same material with different physical properties, such asdoping concentration, dopant type, defect type or density, mismatch typeor density, or other properties.

In some embodiments, the sixth ARC 401, the seventh ARC 403, and theeighth ARC 405 may each comprise the same material, but the precursorflow rates may be different during formation of each of the sixth ARC401, the seventh ARC 403, and the eighth ARC 405 such that each of thesixth ARC 401, the seventh ARC 403, and the eighth ARC 405 has differentindex of refraction. For example, the sixth ARC 401, the seventh ARC403, and the eighth ARC 405 may each be silicon nitride, but the flowrate of the precursors of each may be different to form silicon nitridehaving different indices of refraction. For example, silicon nitride maybe formed using SiH₄ as a first precursor, N₂ as a second precursor, andNH₃ as a third precursor, and the sixth ARC 401 may be formed with afirst precursor flow rate of between 40 sccm and 300 sccm, such as about110 sccm, a second precursor flow rate of between 2000 sccm and 20000sccm, such as about 8000 sccm, and a third precursor flow rate ofbetween 20 sccm and 300 sccm, such as about 80 sccm so that the sixthARC 401 will have a first refractive index of 1.9.

The silicon nitride of the seventh ARC 403 may be formed with a firstprecursor flow rate of between 40 sccm and 300 sccm, such as about 90sccm, a second precursor flow rate of between 2000 sccm and 20000 sccm,such as about 7000 sccm, and a third precursor flow rate of between 20sccm and 300 sccm, such as about 60 sccm so that the sixth ARC 403 willhave a first refractive index of 2.0. The silicon nitride of the seventhARC 405 may be formed with a first precursor flow rate of between 40sccm and 300 sccm, such as about 60 sccm, a second precursor flow rateof between 2000 sccm and 20000 sccm, such as about 5000 sccm, and athird precursor flow rate of between 20 sccm and 300 sccm, such as about30 sccm so that the sixth ARC 405 will have a first refractive index of2.1.

In some embodiments, the sixth ARC 401, the seventh ARC 403, and theeighth ARC 405 may each comprise the same material, but the formationpressure may be different during formation of each of the sixth ARC 401,the seventh ARC 403, and the eighth ARC 405 such that each of the sixthARC 401, the seventh ARC 403, and the eighth ARC 405 has different indexof refraction. For example, the sixth ARC 401, the seventh ARC 403, andthe eighth ARC 405 may each be silicon nitride, but the formationpressure of each may be different to form silicon nitride havingdifferent indices of refraction. For example, the sixth ARC 401 may beformed with a pressure of 1 torr to have a first refractive index of1.9, the silicon nitride of the seventh ARC 403 may be formed with apressure of 5 torr to have a second refractive index of 2.0, and thesilicon nitride of the eighth ARC 405 may be formed with a pressure of20 torr to have a third refractive index of 2.1.

In some embodiments, the sixth ARC 401, the seventh ARC 403, and theeighth ARC 405 may each comprise the same material, but the formationtemperature may be different during formation of each of the sixth ARC401, the seventh ARC 403, and the eighth ARC 405 such that each of thesixth ARC 401, the seventh ARC 403, and the eighth ARC 405 has differentindex of refraction. For example, the sixth ARC 401, the seventh ARC403, and the eighth ARC 405 may each be silicon nitride, but theformation temperature of each may be different to form silicon nitridehaving different indices of refraction. For example, the sixth ARC 401may be formed with a temperature of 250° C. to have a first refractiveindex of 1.9, the silicon nitride of the seventh ARC 403 may be formedwith a temperature of 350° C. to have a second refractive index of 2.0,and the silicon nitride of the eighth ARC 405 may be formed with atemperature of 410° C. to have a third refractive index of 2.1.

In some embodiments, the sixth ARC 401, the seventh ARC 403, and theeighth ARC 405 may each comprise the same material, but the formationtemperature may be different during formation of each of the sixth ARC401, the seventh ARC 403, and the eighth ARC 405 such that each of thesixth ARC 401, the seventh ARC 403, and the eighth ARC 405 has differentindex of refraction. For example, the sixth ARC 401, the seventh ARC403, and the eighth ARC 405 may each be silicon nitride doped withhydrogen, but may have a different doping concentration to havedifferent indices of refraction. For example, the sixth ARC 401 may beformed with a doping concentration of 1E20/cm³ to have a firstrefractive index of 1.9, the seventh ARC 403 may be formed with a dopingconcentration of 5E20/cm³ to have a second refractive index of 2.0, andthe eighth ARC 405 may be formed with a doping concentration of 1E21/cm³to have a third refractive index of 2.1.

FIG. 5 illustrates a graph 500 showing an example of the quantumefficiency (QE) of a photosensitive diode. First curve 501 depicts theQE for the photosensitive diode with a blue color filter and a singleARC whose thickness has been chosen to maximize QE for only blue light.Second curve 503 depicts the QE for the photosensitive diode with a bluecolor filter and a single ARC whose thickness has been chosen tomaximize QE for all three of blue light, green light, and red light. Asgraph 500 shows, QE can be improved by using an ARC designed for aspecific color of light rather than an ARC designed for multiple colorsof light.

FIGS. 6A-6B illustrate embodiments of a first pixel array 600 and asecond pixel array 650. The first pixel array 600 and second pixel array650 may be part of an image sensor such as image sensor 100. Forexample, the first pixel array 600 and the second pixel array 650 may bepart of pixel array 110 shown in FIG. 1A. The first pixel array 600includes multiple pixel regions, shown in FIG. 6A by a first green pixelregion 601, a first blue pixel region 603, and a first red pixel region605. The first green pixel region 601, the first blue pixel region 603,and the first red pixel region 605 may be similar to the first pixelregion 103, the second pixel region 105, and/or the third pixel region107 as described in the discussion of FIG. 1A. In the embodiment, thefirst green pixel region 601 is associated with green light. Forexample, the first green pixel region 601 may have a green color filterand an ARC designed for green light. Similarly, the first blue pixelregion 603 is associated with blue light and the first red pixel region605 is associated with red light. The first green pixel region 601, thefirst blue pixel region 603, and the first red pixel region 605 may bearranged in a Bayer RGB pattern, a Yotsuba CRGB pattern, or any othersuitable pattern.

FIG. 6A illustrates an embodiment in which the first green pixel region601 has a larger area than the first blue pixel region 603 or the firstred pixel region 605. For example, the first green pixel region 601 mayhave a first width w₁ and the first blue pixel region 603 and first redpixel region 605 may each have a same second width w₂. As shown in FIG.6A, the first green pixel region 601 may have longer first width w₁ thanthe corresponding second width w₂ of the first blue pixel region 603 andthe first red pixel region 605. The first width w₁ may, for example, belonger than the second width w₂ by 1%, 5%, 10%, 100%, or another amount.In an embodiment, the second width w₂ may be between about 0.8 μm andabout 1.5 μm, such as about 1 μm, and the first width w₁ may be betweenabout 1 μm and about 1.3 μm, such as about 1.1 μm. In an embodiment, thearea of the first green pixel region 601 may be between 1 μm² and 1.69μm², such as about 1.21 μm², and the areas of the first blue pixelregion 603 and the first red pixel region 605 may be between 0.64 μm²and 1.1025 μm², such as about 1 μm². In some cases, the larger area ofthe first green pixel region 601 allows the first green pixel region 601to receive more illumination than the first blue pixel region 603 or thefirst red pixel region 605.

In some embodiments, the first green pixel region 601 may comprise or bedefined by one or more implants that have a different width, area, orshape than that of the first blue pixel region 603 or the first redpixel region 605. The implants of the first green pixel region 601 mayalso have a different concentration, implant ion, doping profile, annealtemperature, or other different characteristics than the first bluepixel region 603 or the first red pixel region 605. In other embodimentsthe pixel regions may have other widths or areas. For example, the firstgreen pixel region 601 may have a different width or area than the firstblue pixel region 603, and the first blue pixel region 603 may have adifferent width or area than the first red pixel region 605.

FIG. 6B illustrates an embodiment of a second pixel array 650 includinga second green pixel region 651, a second blue pixel region 653, and asecond red pixel region 655. As shown in FIG. 6B, the second green pixelregion 651 has a different shape than the second blue pixel region 653and the second red pixel region 655. The second green pixel regions 651have an octagonal shape and the second blue pixel region 653 and thesecond red pixel region 655 have square shapes. In some cases, theoctagonal shape of the second green pixel region 651 allows the relativesize of the second green pixel region 651 to be larger and thus receivemore illumination than the second blue pixel region 653 or the secondred pixel region 655. In some embodiments, the second green pixel region651 may comprise or be defined by one or more implants that have adifferent width, area, or shape than that of the second blue pixelregion 653 or the second red pixel region 655. The implants of thesecond green pixel region 651 may also have a different concentration,implant ion, doping profile, anneal temperature, or other differentcharacteristics than the second blue pixel region 653 or the second redpixel region 655. In other embodiments, the pixel regions may have othershapes or be arranged in other patterns. For example, the pixel regionsmay be square, rectangular, octagonal, polygonal, irregular, or othershapes, and have straight or rounded corners.

In some embodiments, each type of pixel region may have a differentshape. For example, the second green pixel region 651 may have anoctagonal shape, the second blue pixel region 653 may have a squareshape, and the second red pixel region 655 may have a rectangular shape.In some embodiments, a single type of pixel region may have more thanone shape. For example, one green pixel region in the pixel array may bean octagon of a first size, and another green pixel region in the samepixel array may be an octagon of a second size. As another example, onegreen pixel region in the pixel array may be a square, and another greenpixel region in the same pixel array may be a rectangle.

By increasing the relative size of the green pixel regions (e.g., thefirst green pixel region 601 or the second green pixel region 651), agreater portion of the incident illumination impinges on the green pixelregions and thus the illumination received by the green pixel regionsmay be increased. In some cases, the illumination received by the imagesensor may have peak intensity near green, and thus increasing therelative area of the green pixel regions may result in increased quantumefficiency or increased the signal-to-noise ratio (SNR) of the imagesensor. Increasing the relative size of the green pixel regions may alsoallow more efficient energy distribution over different pixel regions inthe image sensor, where the energy E (eV) of light with a wavelength λ(nm) is given by:

$E = {\frac{1240\mspace{11mu}{eV}\;{nm}}{\lambda}.}$

FIG. 7 illustrates an example graph 700 showing that increased greenpixel region size may allow a greater signal-to-noise ratio (SNR). Datapoints 701 show the illumination power (arbitrary units) to produceSNR=10 for a given relative green pixel region size. In graph 700, thegreen pixel size is given as the percent increase of a width of a greenpixel region relative to the red and blue pixel regions. As FIG. 7shows, increasing the relative size of the green pixel regions candecrease the illumination to achieve a given SNR.

In some embodiments, one or more of the pixel regions shown in FIGS.6A-B may include one or more of the ARCs shown in FIGS. 1B and 2-4. Forexample, the first green pixel region 601 or the second green pixelregion 651 may include an ARC that is configured to reduce reflectionfrom green light. Likewise, the first blue pixel region 603 or thesecond blue pixel region 653 may include an ARC that is configured toreduce reflection from blue light, and the first red pixel region 605 orthe second red pixel region 655 may include an ARC that is configured toreduce reflection from red light. For example, the first green pixelregion 601 may include second ARC 171, the first blue pixel region 603may include first ARC 161, and the first red pixel region 605 mayinclude third ARC 181. This is an example; other configurations andcombinations of pixel regions and ARCs may be used. In some embodiments,the image sensor is a front-side illuminated image sensor.

By forming different ARCs on different pixel regions, the overallquantum efficiency and/or signal-to-noise ratio of an image sensor maybe improved. In some cases, the use of different ARCs in different pixelregions may reduce cross-talk between the pixel regions, as each pixelregion can be configured or optimized for a different color of light. Apixel region configured for a certain color of light can have a reducedamount of noise due to unwanted color light impinging on the photodiode.As each pixel region may include ARCs configured for certain colors oflight, the thicknesses of each color filter over each pixel region maybe reduced. A thinner color filter may allow the overall thickness ofthe image sensor to be reduced.

In accordance with an embodiment, a method of manufacturing an imagesensor device, the method includes implanting ions in a first region ofa substrate to form a first photosensitive diode; implanting ions in asecond region the substrate to form a second photosensitive diode,wherein the first region is adjacent the second region; depositing afirst layer comprising a first material over the first region, whereinthe first layer is a first anti-reflection coating having firstanti-reflective properties; and depositing a second layer comprising asecond material over the second region, wherein the second layer is asecond anti-reflection coating having second anti-reflective propertiesdifferent from the first anti-reflective properties, and wherein thesecond layer has a same thickness as the first layer. In an embodiment,depositing the first layer includes depositing a first sublayer anddepositing a second sublayer over the first sublayer. In an embodiment,the first sublayer includes the first material. In an embodiment,depositing the second layer includes depositing a third sublayer havinga different thickness than the first sublayer and depositing a fourthsublayer over the third sublayer, the fourth sublayer having a differentthickness than the second sublayer. In an embodiment, the third sublayerincludes the first material. In an embodiment, depositing the firstlayer further includes depositing a fifth sublayer over the secondsublayer, and wherein depositing the second layer further includesdepositing a sixth sublayer over the fourth sublayer. In an embodiment,the second material is different from the first material. In anembodiment, a first area of the first layer in plan view is greater thana second area of the second layer in plan view. In an embodiment, thefirst area is from about 5% to about 100% greater than the second area.

In accordance with another embodiment, a method includes depositing afirst material to a first thickness over a first pixel region in asemiconductor substrate; depositing the first material to a secondthickness over a second pixel region in the semiconductor substrate,wherein the second thickness is different from the first thickness, anddepositing a second material over the first pixel region and the secondpixel region at the same time, wherein a top surface of the secondmaterial above the first pixel region is a same height above thesemiconductor substrate as a top surface of the second material abovethe second pixel region, wherein the first material over the first pixelregion and the second material over the first pixel region are part of afirst anti-reflective coating (ARC) that reduces reflection for a firstwavelength range of incident light, and wherein the first material overthe second pixel region and the second material over the second pixelregion are part of a second ARC that reduces reflection for a secondwavelength range of incident light that is different from the firstwavelength range of incident light. In an embodiment, the first pixelregion has different dimensions than the second pixel region. In anembodiment, the first pixel region has a different shape than the secondpixel region. In an embodiment, the method also includes planarizing thesecond material. In an embodiment, the method also includes implantingions in the first pixel region to form a first photosensitive diode andimplanting ions in the second pixel region to form a secondphotosensitive diode.

In accordance with yet another embodiment, a method includes forming afirst anti-reflective coating (ARC) over a first photodiode in asemiconductor device, the first ARC having a first area in plan view,including depositing a first dielectric material over the firstphotodiode and forming a second ARC over a second photodiode in thesemiconductor device, the second ARC having a second area in plan viewthat is different than the first area, including depositing a seconddielectric material over the second photodiode, wherein the seconddielectric material is different than the first dielectric material,wherein the first ARC has a same thickness as the second ARC. In anembodiment, forming the first ARC further includes depositing the seconddielectric material over the first photodiode, and wherein forming thesecond ARC further includes forming the first dielectric material overthe second photodiode. In an embodiment, the first ARC is adjacent thesecond ARC. In an embodiment, the method further includes forming afirst color filter over the first ARC and forming a second color filterover the second ARC. In an embodiment, the first dielectric material isan oxide and the second dielectric material is a nitride. In anembodiment, forming the first ARC further includes depositing a thirddielectric material over the first photodiode, and wherein forming thesecond ARC further includes forming the third dielectric material overthe second photodiode, wherein the third dielectric material isdifferent than the first dielectric material and the second dielectricmaterial.

In accordance with yet another embodiment, a method includes forming afirst photosensitive diode and a second photosensitive diode in asemiconductor substrate; depositing a first material over the firstphotosensitive diode and the second photosensitive diode; afterdepositing the first material, depositing a second material over thefirst photosensitive diode, the second material being different from thefirst material, wherein a top surface of the first material above thesecond photosensitive diode is exposed after depositing the secondmaterial; forming a first color filter over the first photosensitivediode; and forming a second color filter over the second photosensitivediode, a topmost surface of the first color filter being level with atopmost surface of the second color filter.

In accordance with yet another embodiment, a method includes forming afirst pixel region, a second pixel region and a third pixel region in asemiconductor substrate; depositing a first material over first pixelregion, a second pixel region and a third pixel region; after depositingthe first material, depositing a second material over the first pixelregion and the second pixel region, the second material being differentfrom the first material, wherein a top surface of the first materialabove the third pixel region is exposed after depositing the secondmaterial; after depositing the second material, depositing a thirdmaterial over the first pixel region, the third material being differentfrom the first material and the second material, wherein the top surfaceof the first material above the third pixel region is exposed afterdepositing the third material; forming a first color filter over thefirst pixel region; forming a second color filter over the second pixelregion; and forming a third color filter over the third pixel region, atopmost surface of the first color filter being level with a topmostsurface of the second color filter and a topmost surface of the thirdcolor filter.

In accordance with yet another embodiment, a method includes forming afirst pixel region, a second pixel region and a third pixel region in asemiconductor substrate; forming a first anti-reflection coating (ARC)over the first pixel region, wherein forming the first ARC includes:forming a first dielectric material over the first pixel region, thefirst dielectric material having a first thickness; forming a seconddielectric material over the first dielectric material, the seconddielectric material being different from the first dielectric material,the second dielectric material having a second thickness; and forming athird dielectric material over the second dielectric material; forming asecond ARC over the second pixel region, wherein forming the second ARCincludes: forming the first dielectric material over the second pixelregion, the first dielectric material having the first thickness; andforming the second dielectric material over the first dielectricmaterial, the second dielectric material having the second thickness;forming a third ARC over the third pixel region, wherein forming thethird ARC includes forming the first dielectric material over the thirdpixel region, the first dielectric material having the first thickness;forming a first color filter over the first ARC; forming a second colorfilter over the second ARC; and forming a third color filter over thethird ARC, a topmost surface of the first color filter being level witha topmost surface of the second color filter and a topmost surface ofthe third color filter.

In accordance with yet another embodiment, a method includes: forming afirst photosensitive diode and a second photosensitive diode in asemiconductor substrate; and forming a first anti-reflection coating(ARC) over the first photosensitive diode and a second ARC over thesecond photosensitive diode, where forming the first ARC over the firstphotosensitive diode and the second ARC over the second photosensitivediode includes: depositing a first material over the firstphotosensitive diode and the second photosensitive diode; afterdepositing the first material, depositing a second material over thefirst photosensitive diode, the second material being different from thefirst material, where a top surface of the first material above thesecond photosensitive diode is not covered by the second material afterdepositing the second material; and after depositing the secondmaterial, depositing a third material over the first photosensitivediode, the third material being different from the first material andthe second material, where a top surface of the second material abovethe first photosensitive diode is covered by the third material afterdepositing the third material, where the top surface of the firstmaterial above the second photosensitive diode is not covered by thesecond material while depositing the third material, and where the topsurface of the first material above the second photosensitive diode isnot covered by the third material after depositing the third material.

In accordance with yet another embodiment, a method includes: forming afirst pixel region, a second pixel region and a third pixel region in asemiconductor substrate, where forming the first pixel region, thesecond pixel region and the third pixel region includes: forming a firstphotosensitive diode in the semiconductor substrate in the first pixelregion; forming a second photosensitive diode in the semiconductorsubstrate in the second pixel region; forming a third photosensitivediode in the semiconductor substrate in the third pixel region; forminga first anti-reflection coating (ARC) over the first photosensitivediode, where forming the first ARC includes: forming a first dielectricmaterial over the first photosensitive diode; forming a seconddielectric material over the first dielectric material, the seconddielectric material being different from the first dielectric material;and forming a third dielectric material over the second dielectricmaterial; forming a second ARC over the second photosensitive diode,where forming the second ARC includes: forming the first dielectricmaterial over the second photosensitive diode; and forming the seconddielectric material over the first dielectric material; forming a thirdARC over the third photosensitive diode, where forming the third ARCcomprises forming the first dielectric material over the thirdphotosensitive diode; forming a first color filter over the first ARC,the first color filter having a first thickness; forming a second colorfilter over the second ARC, the second color filter having a secondthickness different from the first thickness; and forming a third colorfilter over the third ARC, the third color filter having a thirdthickness different from the second thickness, a topmost surface of thefirst color filter being level with a topmost surface of the secondcolor filter and a topmost surface of the third color filter.

In accordance with yet another embodiment, a method includes: forming afirst pixel region, a second pixel region and a third pixel region overa semiconductor substrate, where forming the first pixel region, thesecond pixel region and the third pixel region includes: forming a firstphotosensitive diode in the semiconductor substrate in the first pixelregion; forming a second photosensitive diode in the semiconductorsubstrate in the second pixel region; forming a third photosensitivediode in the semiconductor substrate in the third pixel region; andforming a first anti-reflection coating (ARC) over the firstphotosensitive diode, a second ARC over the second photosensitive diode,and a third ARC over the third photosensitive diode, where forming thefirst ARC over the first photosensitive diode, the second ARC over thesecond photosensitive diode, and the third ARC over the thirdphotosensitive diode includes: depositing a first material over thefirst photosensitive diode, the second photosensitive diode and thethird photosensitive diode; after depositing the first material,depositing a second material over the first photosensitive diode and thesecond photosensitive diode, the second material being different fromthe first material, where a thickness of the second material is betweenabout 20 Å and about 5000 Å, and where a top surface of the firstmaterial above the third photosensitive diode is not covered by thesecond material after depositing the second material; and afterdepositing the second material, depositing a third material over thefirst photosensitive diode, the third material being different from thefirst material and the second material, where a top surface of thesecond material above the first photosensitive diode is covered by thethird material after depositing the third material, and where the topsurface of the first material above the third photosensitive diode isnot covered by the third material after depositing the third material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a firstphotosensitive diode and a second photosensitive diode in asemiconductor substrate; and forming a first anti-reflection coating(ARC) over the first photosensitive diode and a second ARC over thesecond photosensitive diode, wherein forming the first ARC over thefirst photosensitive diode and the second ARC over the secondphotosensitive diode comprises: depositing a first material over thefirst photosensitive diode and the second photosensitive diode; afterdepositing the first material, depositing a second material over thefirst photosensitive diode, the second material being different from thefirst material, wherein a top surface of the first material above thesecond photosensitive diode is not covered by the second material afterdepositing the second material; and after depositing the secondmaterial, depositing a third material over the first photosensitivediode, the third material being different from the first material andthe second material, wherein a top surface of the second material abovethe first photosensitive diode is covered by the third material afterdepositing the third material, wherein the top surface of the firstmaterial above the second photosensitive diode is not covered by thesecond material while depositing the third material, and wherein the topsurface of the first material above the second photosensitive diode isnot covered by the third material after depositing the third material.2. The method of claim 1, further comprising: forming a first colorfilter over the first photosensitive diode; and forming a second colorfilter over the second photosensitive diode, a topmost surface of thefirst color filter being level with a topmost surface of the secondcolor filter.
 3. The method of claim 2, wherein a thickness of the firstcolor filter is different from a thickness of the second color filter.4. The method of claim 2, wherein a bottommost surface of the firstcolor filter is above a bottommost surface of the second color filter.5. The method of claim 2, wherein the second color filter is in physicalcontact with the first material and the second material.
 6. The methodof claim 1, wherein a portion of the semiconductor substrate isinterposed between the first photosensitive diode and the first ARC. 7.A method comprising: forming a first pixel region, a second pixel regionand a third pixel region in a semiconductor substrate, wherein formingthe first pixel region, the second pixel region and the third pixelregion comprises: forming a first photosensitive diode in thesemiconductor substrate in the first pixel region; forming a secondphotosensitive diode in the semiconductor substrate in the second pixelregion; forming a third photosensitive diode in the semiconductorsubstrate in the third pixel region; forming a first anti-reflectioncoating (ARC) over the first photosensitive diode, wherein forming thefirst ARC comprises: forming a first dielectric material over the firstphotosensitive diode; forming a second dielectric material over thefirst dielectric material, the second dielectric material beingdifferent from the first dielectric material; and forming a thirddielectric material over the second dielectric material; forming asecond ARC over the second photosensitive diode, wherein forming thesecond ARC comprises: forming the first dielectric material over thesecond photosensitive diode; and forming the second dielectric materialover the first dielectric material; forming a third ARC over the thirdphotosensitive diode, wherein forming the third ARC comprises formingthe first dielectric material over the third photosensitive diode;forming a first color filter over the first ARC, the first color filterhaving a first thickness; forming a second color filter over the secondARC, the second color filter having a second thickness different fromthe first thickness; and forming a third color filter over the thirdARC, the third color filter having a third thickness different from thesecond thickness, a topmost surface of the first color filter beinglevel with a topmost surface of the second color filter and a topmostsurface of the third color filter.
 8. The method of claim 7, wherein thethird dielectric material is different from the first dielectricmaterial.
 9. The method of claim 8, wherein the third dielectricmaterial is different from the second dielectric material.
 10. Themethod of claim 7, wherein the first dielectric material of the firstARC, the first dielectric material of the second ARC and the firstdielectric material of the third ARC are formed using a same depositionprocess.
 11. The method of claim 7, wherein the second dielectricmaterial of the first ARC and the second dielectric material of thesecond ARC are formed using a same deposition process.
 12. The method ofclaim 7, wherein the first pixel region and the second pixel region havedifferent areas.
 13. The method of claim 7, wherein the first pixelregion is a green pixel region and the second pixel region is a bluepixel region, and wherein a width of the first pixel region is greaterthan a width of the second pixel region.
 14. A method comprising:forming a first pixel region, a second pixel region and a third pixelregion over a semiconductor substrate, wherein forming the first pixelregion, the second pixel region and the third pixel region comprises:forming a first photosensitive diode in the semiconductor substrate inthe first pixel region; forming a second photosensitive diode in thesemiconductor substrate in the second pixel region; forming a thirdphotosensitive diode in the semiconductor substrate in the third pixelregion; and forming a first anti-reflection coating (ARC) over the firstphotosensitive diode, a second ARC over the second photosensitive diode,and a third ARC over the third photosensitive diode, wherein forming thefirst ARC over the first photosensitive diode, the second ARC over thesecond photosensitive diode, and the third ARC over the thirdphotosensitive diode comprises: depositing a first material over thefirst photosensitive diode, the second photosensitive diode and thethird photosensitive diode; after depositing the first material,depositing a second material over the first photosensitive diode and thesecond photosensitive diode, the second material being different fromthe first material, wherein a thickness of the second material isbetween about 20 Å and about 5000 Å, and wherein a top surface of thefirst material above the third photosensitive diode is not covered bythe second material after depositing the second material; and afterdepositing the second material, depositing a third material over thefirst photosensitive diode, the third material being different from thefirst material and the second material, wherein a top surface of thesecond material above the first photosensitive diode is covered by thethird material after depositing the third material, and wherein the topsurface of the first material above the third photosensitive diode isnot covered by the third material after depositing the third material.15. The method of claim 14, wherein forming the first pixel region, thesecond pixel region and the third pixel region further comprises:forming a first color filter over the first photosensitive diode;forming a second color filter over the second photosensitive diode; andforming a third color filter over the third photosensitive diode, atopmost surface of the first color filter being level with a topmostsurface of the second color filter and a topmost surface of the thirdcolor filter.
 16. The method of claim 15, wherein a thickness of thethird color filter is greater than a thickness of the second colorfilter.
 17. The method of claim 15, wherein the thickness of the secondcolor filter is greater than a thickness of the first color filter. 18.The method of claim 14, wherein the first pixel region has a differentshape than the second pixel region.
 19. The method of claim 14, whereina thickness of the first material is between about 20 Å and about 5000Å.
 20. The method of claim 14, wherein a thickness of the third materialis between about 20 Å and about 5000 Å.